REVIEWARTICLE

Acromioclavicular joint injuries and reconstructions: a reviewof expected imaging findings and potential complications

Andrew C. Kim & George Matcuk & Dakshesh Patel &John Itamura & Deborah Forrester & Eric White &

Christopher J. Gottsegen

Received: 9 April 2012 /Accepted: 10 May 2012 /Published online: 26 May 2012# Am Soc Emergency Radiol 2012

Abstract Shoulder injuries, including acromioclavicular(AC) joint separations, remain a common reason for presen-tation to the emergency room. Although the diagnosis canbe made apparent through proper history and physical ex-amination by the emergency medicine physician, ascertain-ing the degree of injury can be difficult on the basis ofclinical evaluation alone. While there is consensus in theliterature that low-grade AC joint injuries can be treatedwith conservative management, high-grade injuries willgenerally require surgical intervention. Furthermore, thetreatment of grade 3 injuries remains controversial, makingit incumbent upon the radiologist to become comfortablewith distinguishing this diagnosis from lower or highergrade injuries. Imaging of AC joint injuries after clinicalevaluation is generally initiated in the emergency roomsetting with plain film radiography; however, on occasion,an alternative modality may be presented to the emergencyroom radiologist for interpretation. As such, it remains im-portant to be familiar with the appearance of AC jointseparations on a variety of modalities. Another possiblepatient presentation in both the emergent and nonemergentsetting includes new onset of pain or instability in thepostsurgical shoulder. In this scenario, the onus is oftenplaced on the radiologist to determine whether the pain orinstability represents the sequelae of reinjury versus a com-plication of surgery. The purpose of this review is to presentan anatomically based discussion of imaging findings

associated with AC joint separations as seen on multiplemodalities, as well as to describe and elucidate a variety ofpotential complications which may present to the emergencyroom radiologist.

Keywords Acromioclavicular joint separation . Rockwoodclassification . Hardware failure . Late osteoarthrosis

Introduction

Traumatic injuries, including fractures and dislocations, re-main among the most common reasons for a visit to theemergency room in the USA today [1]. Among these inju-ries, AC joint separations encompass up to 12 % of dislo-cations involving the shoulder [2]. This type of injury isparticularly common among young male athletes, who havea five-time greater incidence over their female counterparts[2]. Proper clinical history, in conjunction with physicalexamination findings, may illuminate the diagnosis forth-right. However, in many cases, the role of imaging remainsparamount in the proper diagnosis and classification ofshoulder injuries and in particular AC separations. Withregards to AC separations, the most common mechanismof injury involves a blow to the acromion with the shoulderin the adducted position. A predictable pattern of traumatictearing ensues, beginning with disruption of the AC liga-ments, followed by the joint capsule, the coracoclavicular(CC) ligaments, and finally the deltotrapezial fascia [3].This is usually due to a direct force mechanism of injuryfrom a fall onto the superolateral aspect of the shoulder [3].Activities commonly associated with this type of injuryinclude a variety of sports in which traumatic contact iscommon, such as tackle football or falling from a bike while

A. C. Kim (*) :G. Matcuk :D. Patel : J. Itamura :D. Forrester :E. White :C. J. GottsegenKeck School of Medicine, University of Southern California, LAC+USC Medical Center,1200 North State Street, D+T Room 3D321,Los Angeles, CA 90033, USAe-mail: andrewk@usc.edu

Emerg Radiol (2012) 19:399–413DOI 10.1007/s10140-012-1053-0

cycling. AC separations are particularly common amongstfootball players, with the reported incidence of AC separa-tions among shoulder injuries in this population accountingfor around 40 % overall [4]. Indirect mechanisms of injuryare also possible, including a superiorly directed force dueto a fall onto an outstretched hand or elbow, a history that iscommon to a variety of different osseous and ligamentousinjuries other than AC joint separation. The most commoninitial complaint among patients who have sustained thisinjury is pain, which can be extreme in nature. Physicalexamination findings can vary with the degree of injury,although the most frequent include regional swelling and/or bruising.

Despite what may seem to be a readily apparent clinicaldiagnosis, imaging remains an important component of thecomplete workup of AC joint separation due to potentialsurgical implications, which are based upon the grade ofinjury. Plain radiography has continued to be the mainstayof initial imaging for this type of suspected injury in both theemergency room and ambulatory settings. However, evalu-ation of higher-grade injuries, including of potential liga-mentous injury, may require the use of additional imagingmodalities such as multidetector computed tomography(MDCT) or magnetic resonance imaging (MRI). Specif-ically, MDCT can be helpful in situations that requireprecise delineation of the alignment of the joint, whichis not sufficiently demonstrated on plain radiography.MRI provides superior evaluation of the integrity ofthe ligaments as well as other soft tissue injury. Whilethe role of ultrasound in the evaluation of acute trau-matic shoulder injuries as well as arthritic changes ofthe AC joint has been described, its utilization remainslimited, most likely secondary to a number of confound-ing factors for use in the emergency room setting.These include the availability of the proper ultrasoundtransducers, as well as the necessity for proper tech-nique and methodology when evaluating the AC joint,which is currently not widely taught [5, 6].

The purpose of this review is to (1) discuss the anatom-ical basis for the classification of various types of acromio-clavicular joint separations, including important points ofdifferentiation between each grade, (2) review the differenttreatment options for these injuries, including the controver-sial grade 3 injury, (3) describe what can be expected to beseen by the radiologist on post-surgical imaging, and (4)demonstrate different complications for which patients maypresent to the emergency radiologist such that the imagingappearances are familiar when investigating the source ofpain in the postoperative patient. We will first review theanatomy of the shoulder, including key anatomical land-marks and how these are optimally imaged. We will thenpresent the current accepted classification scheme for acro-mioclavicular joint separations, the Rockwood classification

system. Finally, we will describe and show the surgicalrepair of higher-grade acromioclavicular joint separationsas well as their postoperative complications on plain radi-ography, as this is the most commonly utilized initial mo-dality for imaging acute shoulder pain in the emergencyroom setting.

Normal anatomy of the AC joint

The AC joint is principally formed by the lateral margin ofthe distal clavicle and the medial surface of the acromion.An articular disc may be present between the articularsurfaces. When present, typically, the disc incompletelyseparates the osseous structures, although on occasion com-plete separation can be seen. When the separation doesoccur, it is usually along the superior margin of the articu-lation. However, frequently, this articular disc is not present.Surrounding the articular margin, there is a joint capsule,which is lined by a synovial membrane [7]. In conjunctionwith this capsule are two ligaments located above and belowthe joint known as the superior and inferior AC ligaments.These structures provide restraint against horizontal transla-tion of the joint [8].

The coracoclavicular (CC) ligament consists of two sep-arate components: the conoid ligament and the trapezoidligament. The conoid ligament is located medial to thetrapezoid ligament, and the two are separated by either fator a bursa. This ligament is conical in shape, with densefibers that broadly span from the apical attachment at thebase of the coracoid to its base at the conoid tubercle alongthe undersurface of the clavicle at the junction of the midand lateral thirds. The apex of this ligament is locatedposteromedial to the trapezoid ligament and lateral to thescapular notch, coursing in a spiral fashion superiorly andnearly vertical in orientation [7]. The primary function of theconoid ligament is to resist anterosuperior clavicle transla-tion and rotation. The trapezoid ligament is the anterolateralfasciculus of the coracoclavicular ligament and is quadrilat-eral in shape. The principal source of resistance againstposterior displacement of the clavicle, it also renders someresistance to superior, inferior, and anterior forces [9]. Thin-ner than the conoid ligament, its inferior attachment is foundalong the superior surface of the coracoid process, while itssuperior attachment is to the oblique ridge of the undersur-face of the clavicle. The ligamentous anatomy of the acro-mioclavicular joint is illustrated in Fig. 1.

Two muscular attachments to the acromion that are worthnoting are the trapezius and deltoid muscle attachments.Both muscles have attachments to the acromion and thescapular spine. The trapezius has its insertion on the supe-rior aspect of these two osseous structures, while the deltoidhas origins from the inferolateral aspect of both structures.

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Along the spectrum of AC joint injuries, a defect in thedeltotrapezial fascia is indicative of a significant injury [3].

Imaging of the AC joint

As with many direct blow injuries in the emergency roomsetting, initial imaging of the AC joint is usually performedvia plain radiography. The normal distance between thedistal clavicle and the acromion ranges from approximately1 to 6 mm, while the normal coracoclavicular distance isapproximately 11 to 13 mm [2]. Due to the nature of themost common mechanism of injury, that being direct forcetrauma, unilateral separation is suspected in most instances.However, the AC joints should ideally be imaged bilaterally,even when unilateral injury is suspected. This is due to thenatural anatomic variation inherent to this joint, requiringthe opposite side for comparison [10]. The importance ofbilateral imaging of the AC joints in cases of suspectedseparation is demonstrated in Fig. 2. An AP view of theAC joints with or without cephalic tube angulation serves asthe standard for initial imaging. While a straight AP viewallows for more anatomical positioning of the joint, angulat-ing the tube in a cephalic direction does have the advantageof projecting the AC joint with increased separation fromthe proximal aspect of the acromion [10]. Considerationshould be given to reducing radiation dose to the patientduring imaging. Different exposure methods can be utilized

in this regard, though the method of choice is generallyfacility dependent. As AC separations are an injury that ismore commonly present in young patients, careful attentionto minimizing radiation dose to the patient’s thyroid gland isalways prudent. At our institution, we utilize a separateexposure method, in which the images are coned down tothe AC joint utilizing a single cone with imaging of the twosides performed separately. Inherently, this method reducesthe radiation dose to the patient’s thyroid as it is not directlyexposed to the radiation beam. The primary disadvantage ofthis method, however, is that separate exposures allow forincreased variance between projections, which may renderthe images untenable for comparison. As an alternative toseparate exposures, a customized binocular cone may beused to simultaneously image the AC joints while alsominimizing radiation exposure to the patient’s thyroid byavoiding direct beam exposure. However, as this type ofcone is not widely available in general practice, this view isnot routinely obtained.

On occasion, it may be helpful to further exaggerate thesuspected separation by utilizing other views. To this end, aweight-bearing or stress view is utilized at some institutions,including our own, to help differentiate between grades ofinjury. In particular, this view is thought to be helpful indifferentiating between grade 2 and 3 separations. It mayalso be useful in ascertaining whether or not a separationtruly exists. However, the ultimate utility of the weight-bearing view is somewhat controversial. A study performedby Bossart et al. [11] found that weight-bearing views wereonly able to reveal a higher-grade injury in 4 % of cases,which would indicate that this view is of limited clinicalvalue. In addition, an analysis performed by Vanarthos et al.[12] on cadaveric models showed that an AP view with theshoulder in internal rotation may occasionally be sufficientfor diagnosis of grade 3 injuries, thus alleviating the poten-tial pain that would be experienced by a patient with anacute shoulder injury during a weight-bearing view. Further-more, the method by which the weight-bearing view isperformed has also provoked some controversy, with differ-ences of opinion over whether it is appropriate to have thepatient hold weights in his/her hands versus having theweights hanging from the wrists. While theoretically hold-ing the weights can cause contraction of the trapezius mus-cle and reduce the visibility of a separation [13], a studyevaluating the difference in effect under real-time ultrasoundshowed no significant difference in the amount of distrac-tion when comparing hand-held weights versus weightswhich were suspended from the wrists [14]. Regardless,the weight-bearing view is performed either by having thepatient hold weights (e.g., sandbags) or suspending theweights from the patient’s wrists, with each weight weigh-ing approximately 10–15 lbs. A difference in craniocaudalmeasurement of >3 mm from the nonweight-bearing view is

2 3 4

7

10

11

6

9

51

8

1. Clavicle2. Conoid ligament3. Trapezoid ligament4. Superior and inferior

acromioclavicularligaments

5. Acromion6. Coracoid process7. Coracoacromial ligament8. Coracohumeralligament9. Scapula10. Greater tuberosity11. Intertubercular groove

Fig. 1 The ligamentous anatomy of the acromioclavicular joint. Theacromioclavicular (AC) joint is a complex joint with numerous liga-mentous support structures. Of particular importance when assessinginjuries to the AC joint are the acromioclavicular ligaments [4] and thecoracoclavicular ligament, which is composed of the conoid and trap-ezoid ligaments [2, 3]. In addition to these ligaments, an articular discmay be present between the clavicle and the acromion. The normal ACinterval is approximately 1–6 mm. The normal CC interval is approx-imately 11–13 mm. Additional structures are as labeled

Emerg Radiol (2012) 19:399–413 401

considered abnormal (Fig. 3) [15]. As another alternative tothe weight-bearing view, advanced imaging modalities suchas MDCT can provide a more detailed analysis of osseousdisplacement, though at the cost of increased radiation ex-posure to the patient.

Another view that can be useful is a Zanca view (Fig. 4).In order to obtain a Zanca view, the X-ray tube is centered atthe AC joint with a 10–15 ° cephalic tilt. The standardkilovoltage is also decreased up to 50 % in order to bettervisualize the soft tissues and to increase joint detail [10]. Ifthere is continued suspicion for an AC joint separation, butthe separation remains poorly demonstrated on the standardviews, additional stress views while placing the patient’sarm on the affected side in a variety of positions may helpaccentuate the separation. A potential confounding factor inthe diagnosis of AC joint injury in the emergency roomsetting is that patients may be imaged at the bedside while

recumbent or at an angle other than the upright position.Placing the patient in an erect position not only properlyorients the patient for the exam but also allows gravity toassist in demonstrating the separation.

Advanced methods for imaging the AC joint include CTand MRI. CT image acquisition is generally straightforwardas imaging in the transaxial plane utilizing bone and softtissue windows can be reconstructed in the sagittal andcoronal planes. In addition, 3D volume rendering can behelpful in difficult cases to improve visualization of thedegree and trajectory of bony displacement. Furthermore,CT may better demonstrate subtle fractures, which can bemissed on the plain radiographs. However, while subtlefractures may be more readily apparent on CT, the findingscompatible with AC joint separation are similar to those ofplain film radiography but with the disadvantage of a muchlarger radiation dose to the patient. In general, CT is best

Fig. 2 Bilateral imaging. It isideal to image the AC jointsbilaterally when a separation issuspected, even when the injuryis thought to be unilateral. a APview, b Zanca view, and caxillary views of the rightshoulder. This patient presentedafter falling from his bicycleonto his shoulder. There isapparent inferior displacementof the acromion relative to theposition of the clavicle. Thiswas initially diagnosed as agrade 3 AC separation. d Zancaviews of the bilateral shouldersdemonstrate a symmetricappearance to the AC joints,indicating the position of theacromion relative to the distalclavicle is likely normalanatomy for this patient

Fig. 3 Non-weight-bearing vs. weight-bearing views. AP views of theleft clavicle a without weight-bearing/arm in external rotation and bwith weight-bearing/arm in internal rotation. Note the increased dis-placement between the clavicle and the acromion in this patient with agrade 1 AC separation. The weight-bearing view is obtained with a 10–15-lb weight hanging from the patient’s wrist in an attempt to

exaggerate the distance between the distal clavicle and the acromionin more subtle cases. A difference in measurement of the AC distanceof >3 mm between the two views is considered abnormal. Note thatplacing the arm in internal rotation can help to facilitate visualization ofthis difference

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reserved for cases in which there is a higher index ofsuspicion for a fracture rather than an AC separation. MRIis an ideal imaging modality for soft tissue evaluation,especially ligamentous injury. Sequence acquisition variesbetween various institutions, and satisfactory images can beobtained on a 1.5-T or a 3-T magnet, both of which areutilized at our institution. As an example, our image acquis-itions of the AC joint comprise of the following sequences,which are modified from our shoulder MRI protocol with anextended field of view to visualize more medial structures:coronal T1, T1 with fat saturation (fat sat), and T2 fat sat,sagittal T1 fat sat, axial T1 fat sat, and an axial oblique T1fat sat. The normal anatomy of the coracoclavicular liga-ment is best demonstrated on T1-weighted (T1W) imagesdue to high contrast to noise, whereas on T2-weighted fatsaturated images, these structures are slightly more difficultto delineate. Conversely, in the setting of injury, the edemarelated to trauma around these ligaments allows for im-proved identification of their fibers on T2 fat sat andintermediate-weighted, fat-saturated MR images, whilethese structures may become less conspicuous on the T1Wimages (Fig. 5) [9]. As a supplement, administration ofintravenous gadolinium can further assist in depicting thepath and full extent of soft tissue injury in fine detail [9]. It

has been suggested that patients with more advanceddegrees of injury requiring surgical reconstruction may ben-efit from having an MRI performed prior to surgery todefine the full extent of injury, though the role of MRI inAC separations is not clearly defined [9]. Overall, MRIprovides incomparable detail of the anatomy of the softtissues surrounding the AC articulation. As a caveat regard-ing both CT and MR imaging, it is important to rememberthat the study is acquired with the patient in a recumbentposition. Thus, the relative positions of the clavicle andacromion may be altered, particularly in less severe injuries.Furthermore, the advantage of gravitational assistance gar-nered from having the patient in an upright position whenacquiring radiographs is lost, which again may mask the trueextent of separation.

Classification of injuries

The original classification of AC joint separations was firstdescribed by Tossy and Allman in the 1960s [16, 17]. Thisclassification scheme divided AC joint separations into threeseparate grades based primarily on the position of the distalclavicle relative to the acromion. An injury was consideredgrade 1 if the distal clavicle demonstrated normal anatomi-cal alignment with the acromion, indicating only a sprain ofthe ligamentous structures. A grade 2 injury involved dis-placement of the clavicle that was <100 % of the clavicularwidth. This type of injury was thought to be associated withrupture of the AC ligaments and sprain of the otherwiseintact CC ligaments. An injury was considered grade 3when there was displacement of the distal clavicle >100 %of its width with a simultaneous 25–100 % increase in thecoracoclavicular distance. The AC and CC ligaments wereboth considered ruptured in this type of injury. From this

Fig. 4 The Zanca view. This view is obtained through a tube angula-tion of 10–15 ° cephalad while also decreasing the standard kilovoltageby up to 50 %

C AC

c

ba

Fig. 5 MRI anatomy of the AC joint. a Oblique coronal T1-weightedimage of the left AC joint, profiling the superior (long black arrow)and inferior (white arrow) acromioclavicular ligaments. A portion ofthe intraarticular disc is visible (short black arrow). A acromion, Cclavicle. b Oblique coronal T1-weighted image located anterior to the

first image demonstrates the conoid (short black arrow) and trapezoid(long black arrow) portions of the coracoclavicular ligament. Noticethat these two components are separated by a small amount of fat(white arrow). C clavicle, c coracoid

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original classification system, modifications were made byRockwood et al. in 1989 [18], bringing about the classifica-tion system that is currently used in practice by radiologists.This classification system involves six different grades ofAC joint separation. A summary of the Rockwood classifi-cation system along with pertinent radiographic findingsassociated with each grade can be found in Table 1.

Grade 1 injury

Grade 1 injuries of the AC joint can be difficult for theemergency radiologist to appreciate without the proper clin-ical context, as the joint may appear normal on plain radi-ography. An injury is considered grade 1 when there is asprain of the AC ligaments without a complete tear.

Clinically, patients with this type of injury may present withtenderness (with or without swelling) in the region of theAC joint. However, typically, there is no tenderness in thearea of the CC interspace. While this type of injury may beseen to better advantage on MRI, plain radiography is oftenthe initial and only modality encountered by the emergencyradiologist. On radiographs, findings include possible mildswelling or edema of the soft tissues overlying the AC joint.The joint itself is often normal in appearance (Fig. 6). Thistype of injury is suggested when there is >2 mm separationbetween the distal clavicle and the acromion. However, itshould be noted that this measurement is confounded by a

Table 1 Summary of the Rockwood classification system of AC separation and radiographic findings

Grade ACligaments

CC ligament

CC interval

Radiographic appearance of the AC Joint

tearOften normal.Pertinent clinical history required for

diagnosis.MRI better demonstrates the injury.Most common type of AC separation.

Widening of the AC joint space may be seen due to horizontal instability.

<25% inferior displacement of the acromion.

IncreaseWidening of the AC joint space which may

be more severe than in grade-2 type injury.25-100% inferior displacement of the

acromion.

IncreaseBest seen on axillary view.Posterior translation of the distal clavicle.Inferior displacement of the acromion

varies with degree of CC ligament injury.Rare.

IncreaseFindings similar to but more severe than

grade 3-type injury due to complete disruption of supporting ligaments.

>100% inferior displacement of the acromion.

1 Sprain/partial Normal Normal

2 Torn Sprain <25%Increase

3 Torn Torn 25-100%

4 Torn Torn Variable

5 Torn Torn >100%

6 Torn Intact Decrease Subacromial or subcoracoid location of the distal clavicle.

Look for concomitant fractures of the clavicle or of the nearby ribs.

Fig. 6 Anteroposterior (AP) view of a grade 1 separation. As in thiscase, despite the patient’s complaining pain and an appropriate clinicalhistory, the AC joint often appears radiographically normal

Fig. 7 Coronal short tau inversion recovery (STIR) image of the leftshoulder in a patient with a grade 1 AC separation. There is bulging ofthe AC ligaments secondary to joint inflammation and edema, asindicated by increased signal within the joint space (arrow)

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number of factors that are often encountered by the emer-gency radiologist including suboptimal imaging techniqueor patient positioning. When this type of injury is suspected,it can be helpful to obtain a dedicated AC joint image suchas the previously described Zanca view or a comparisonview of the contralateral side. A weight-bearing view mayfurther assist in confirming the diagnosis. However, if radio-graphs are normal and there is continued clinical suspicionfor a grade 1 injury, an MRI can be a helpful and moredefinitive examination. As demonstrated in Fig. 7, fluid-sensitive MRI sequences such as short tau inversion recov-ery can vividly demonstrate edema about the AC joint withdistension of the capsule, findings that are consistent with asprain. MRI can also be utilized to demonstrate a completeligamentous tear, the presence of which would disqualifythe injury for classification as a grade 1 injury. However, itis important to note that while MRI can be a useful exam-ination, there are no specific signs on MRI that indicate a

grade 1 separation. This is especially true in adult patients,as signal abnormalities in the region of the AC joint are acommon finding [9]. Overall, this is the most common typeof AC joint injury encountered in clinical practice, and assuch, it is important for the emergency radiologist to remainmindful of this diagnosis.

Grade 2 injury

Grade 2 injuries are another common type of AC jointseparation, which are often more clinically apparent thanthe grade 1 injury. Together with grade 1 separations, theyoccur twice as frequently as the remaining grades of injury[19]. In a grade 2 injury, there is disruption of the AC jointcapsule with tearing of the AC ligaments, causing horizontalinstability. The CC ligaments remain intact. The patientusually presents with tenderness and swelling over the ACjoint, similar to a grade 1 injury. However, unlike with agrade 1 injury, there is also point tenderness over the CCinterval. As the CC ligaments are still intact, vertical stabil-ity is overall preserved, and elevation of the distal clavicle isusually not well appreciated on physical examination. Onplain radiography, the AC joint is disrupted with wideningof the AC joint space. While widening of the CC interspacemay also be present, the increase in distance should be<25 % [9] (Fig. 8).

Grade 3 injury

Although grade 1 and 2 injuries are the most common typeof AC joint separation, grade 3 injuries are still relatively

Fig. 8 AP view of a grade 2 separation. Grade 2 separations involvedisruption of the AC joint, with horizontal instability and minimal orabsent vertical instability. Findings include possible widening of theAC joint (solid arrows) with <25 % increase in the CC interval (dashedarrows)

Fig. 9 AP view of a grade 3 separation. Grade 3 separations are moresevere than grade 2. There may again be widening of the AC jointspace (solid arrows). However, the distinguishing feature of a grade 3separation is a tear of the CC ligament, with resulting 25–100 %increase in the CC interspace (dashed arrows)

Fig. 10 Grade 4 separation. Axillary view of the left AC joint dem-onstrating posterior displacement of the distal clavicle. Grade 4 sepa-rations are distinguished by posterior displacement of the clavicle intoor through the trapezius muscle. This displacement is best appreciatedon an axillary view. Clinically, the AC joint will be irreducible, withprominence of the anterior acromion. In patients with suspected grade4 injury, it is important to evaluate the sternoclavicular joint for apossible bipolar clavicular dislocation

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frequently encountered, reportedly comprising up to 40 % ofAC separations [20]. In grade 3 injuries, there is furtherprogression along the spectrum of ligamentous disruption.Along with tearing of the AC ligaments, grade 3 separation

involves tearing of the CC ligaments as well as a highergrade tearing of the AC joint capsule. Patients with this typeof injury present with symptoms of pain and restrictedmotion of the affected side. On physical examination, thedistal clavicle is often prominent in appearance and presentsas a palpable bump due to cranial translation. While there iselevation of the distal clavicle relative to the acromion, thedisplacement is reducible. Radiographically, there is widen-ing of the AC joint as well as a 25–100 % increase in thesize of the CC interspace (Fig. 9). In general, this grade ofseparation can usually be seen without the assistance ofweights. This type of injury should be distinguished froma fracture of the articular surface of the distal clavicle. Theseinjuries can share a common history of direct blow traumaas well as an appearance of displacement at the articularsurface on plain radiography. As the fracture may be subtle,it can be difficult to distinguish these two entities. However,unlike a grade 3 separation, the articular fracture does notinherently involve disruption of the ligaments about the ACjoint. Interestingly, the management strategies of grade 3separations and intraarticular fractures of the lateral third ofthe clavicle are both controversial and with significant over-lap, with advocates of nonoperative and operative manage-ment in the literature for both types of injury. Conservative

a

b

c

Fig. 11 Floating clavicle. a APview of the right clavicledemonstrates a readily apparentAC separation. There is alsodisruption of thesternoclavicular joint (arrow),though this is more difficult toappreciate due to overlappingshadows on this view. b Angledview demonstrates thisdisarticulation to betteradvantage. Note the relativeposition of the proximal rightclavicle compared to theopposite side (circles). c 3Dsurface rendered reconstructionfrom a CT scan betterdemonstrates the separation ofboth the right AC and SC joints,causing the clavicle to be“floating”

Fig. 12 AP view of a grade 5 separation. In grade 5 separations, thereis complete disruption of all of the stabilizing ligaments of the ACjoint. There is >100 % increase in the CC interspace (arrows). Thisappearance implies extensive detachment of the deltoid and trapeziusmuscles and fascia. Unlike a grade 3 separation, clinically these sepa-rations are irreducible. A focus of heterotopic ossification is seeninferior to the distal clavicle, consistent with chronic injury

406 Emerg Radiol (2012) 19:399–413

management for both injuries involves a sequence of immo-bilization followed by structured rehabilitation, while oper-ative management involves different types of fixation withor without distal clavicular resection, with varying degreesof success [21]. Evaluation of the joint with additional viewscan often be helpful in differentiating these two entities, oralternatively, CT can be useful to definitively identify afracture line or a fracture fragment. Management optionsfor grade 3 injuries are discussed later under “Treatmentoptions.”

Grade 4 injury

Overall, grade 4 AC separations are relatively rare in clinicalpractice. Grade 4 injuries involve AC joint separation withdisplacement of the distal clavicle into or through the trape-zius muscle. Unlike a grade 3 injury, this type of separationcannot be reduced, and on physical examination, there maybe prominence of the anterior acromion. Radiographs cansufficiently demonstrate the posterior translation of the dis-tal clavicle, and an axillary view is ideal for demonstratingthis translation to greatest effect (Fig. 10). Although overallneurovascular injuries are uncommon in the setting of ACseparation without a concomitant injury to the shouldergirdle [22], grade 4 injuries can be associated with damageto the ipsilateral brachial plexus [3]. In addition to symp-toms of pain and alteration of motion in the affected shoul-der, patients can present with symptoms of brachialplexopathy, ranging from mild weakness and numbness tocomplete lack of feeling and movement in the ipsilateralarm. As such, an MRI of the brachial plexus may be neces-sary in the context of clinical symptoms suggestive of anassociated injury.

Bipolar clavicle dislocation

When evaluating a grade 4 injury, it is important to viewboth the proximal and distal ends of the clavicle to not onlysearch for AC joint pathology but also to assess the align-ment of the sternoclavicular (SC) joint. This is important inorder to exclude the possibility of a bipolar clavicular dis-location (Fig. 11). Such bipolar dislocations of the clavicleare rare and are usually associated with an indirect mecha-nism of high-energy trauma, such as an impactful blow tothe lateral aspect of the shoulder or truncal torsion withsimultaneous pressing together of the shoulders [23]. Thesetypes of injuries can be referred to by a variety of names,including traumatic floating clavicle, panclavicular disloca-tion, or bifocal clavicle dislocation [24]. Treatment of thistype of injury can range from conservative management inthe asymptomatic patient to open reduction and internalfixation in patients with pain, instability, or requirementsof higher functionality. In chronic cases, this type of injuryhas also been treated with total claviculectomy [24]. It iscrucial for the emergency radiologist to recognize this entitywhen present, as overlooking the bipolar nature of the injurycan result in insufficient management by directing the focusof the surgeon’s attention to a single area of separation,leading to poor functional outcomes.

Grade 5 injury

With grade 5 injury, there is further propagation of damageto the supporting structures, including complete disruptionof all of the stabilizing ligaments of the AC joint as well asextensive detachment of the deltoid and trapezius musclesand fascia. Similar to a grade 3 injury, there is elevation of

Table 2 Treatment options for AC separations by grade

Grade of Injury Management

1-2 Conservative management with variable periods of immobilization followed by physical rehabilitation.

Typically do not require surgery.Chronic injuries with severe arthritic changes and/or pain

may be treated with distal clavicle resection.

3 Controversial. No consensus within the surgical or physical rehabilitation medicine literature.

Patient may be started on conservative therapy and have surgery later if conservative management is unsuccessful in producing a favorable outcome.

Surgery may be favored in high-performance athletes.

4-6 Typically require surgical management.Preferred surgical reconstruction varies by institution and

depends on grade of injury.

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the distal clavicle relative to the acromion, although withgrade 5 injury >100 % CC interspace widening can be seen.The cranial translation of the distal clavicle can be markedon clinical exam, with subcutaneous positioning of theclavicle noted on physical exam. Unlike a grade 3 injury,this AC joint separation is irreducible on physical exam(Fig. 12).

Grade 6 injury

A grade 6 injury occurs when there is separation of the ACjoint with displacement of the distal clavicle into a subacro-mial or subcoracoid position. Often, a history of high-impact trauma while the patient’s shoulder is in an external-ly rotated, hyperabducted position can be elicited. Given theassociation with high-energy trauma, these injuries often areseen with multiple fractures of the ribs and the clavicle [3].Much like the grade 4 injury, which also involves multi-planar displacement of the distal clavicle, the subcoracoiddisplacement of the distal clavicle has an increased inci-dence of associated brachial plexus and/or vascular injury.In the context of clinical symptoms such as numbness in theextremity, an MRI of the brachial plexus can be helpful forfurther evaluation. Furthermore, vascular injury in a patientwith diminished or absent pulses may be assessed with anangiographic examination such as an MR angiogram or aconventional angiogram.

Treatment options

Treatment options for AC joint separations vary dependingon the grade of separation and are summarized in Table 2.Several studies in both the surgical and physical rehabilitation

medicine literature support a conservative approach to man-agement of the grade 1 or 2 separation [25–27]. Severalmethods of management and rehabilitation of the injury havebeen espoused, including a four-phase method of immobili-zation followed by rehabilitation in a study of athletes withlow grade AC joint separations [25]. Occasionally, patientsmay complain of continued pain in the joint following non-surgical management, which may be secondary to the devel-opment of arthritic changes in the joint. In cases wherenonsurgical management fails either due to pain or inappro-priate level of function for the patient’s level of activities,surgery may provide a better result, though these instancesare rare [28]. Additional studies in the surgical literature haveshown the advantage of operative management of grade 4–6injuries [25, 29]. The management of grade 3 injuries remainscontroversial. With studies both in support of and againstsurgical management, a true consensus regarding treatmentof this injury remains elusive [30, 31]. Irrespective of theultimate course of treatment, it remains important to recognizegrade 3 injury so that an appropriate discussion between thepatient and the clinician regarding future management cantake place.

A variety of different surgical methods have been devisedto correct the mechanical and physical derangement associ-ated with this injury, and it is important to be familiar withthese methods in order to appropriately recognize the find-ings on postoperative imaging. The common goal of allmethods of surgical fixation is to reestablish and to maintainanatomical AC joint alignment through open and/or arthro-scopic reduction. In general, these procedures also attemptto repair the deltotrapezial fascia if it is disrupted as well as

Fig. 13 AP view of the left shoulder following hook plate and screwfixation repair of an AC separation. A modified Weaver–Dunn proce-dure was also performed in conjunction with the hook plate repair,though resection of the distal clavicle is not ideally visualized on thisradiograph

Fig. 14 Diagram of a modified Weaver–Dunn procedure with tendonaugmentation. Resection of the distal clavicle is performed in anattempt to prevent osteoarthrosis. The coracoacromial ligament is thenmobilized and sutured into the newly resected distal clavicle for stabi-lization of the joint (circle). Tendon or suture augmentation can furthersupport joint stabilization (arrow). Other methods of enhancing jointstability include tape cerclage or use of other types of graft material

408 Emerg Radiol (2012) 19:399–413

to debride the articulation. A procedure that was utilized inthe past was primary pin fixation to affix the clavicle to thecoracoid base. Although findings related to this proceduremay be encountered in older patients, this method is nolonger utilized secondary to the rare but disastrous compli-cation of pin migration, with case reports of migration intothe great vessels and spinal canal [32, 33]. Primary fixationwith other devices is still performed today, including use ofa hook plate, which is primarily performed in Europe [34,

35] (Fig. 13). This procedure can be performed with orwithout reconstruction of the ligaments. Ligament recon-struction was first described by Weaver and Dunn, and amodified Weaver–Dunn procedure remains a commonchoice among orthopedic surgeons [36, 37] (Figs. 14 and15). As initially described, this procedure involved threeprinciple steps including resection of the distal 2 cm of theclavicle, detaching the acromial attachment of the coracoa-cromial ligament, and suturing this attachment to the distalclavicle [38]. The distal clavicle resection portion of theprocedure attempts to avoid late degenerative changes, astep that has found favorable support in the surgical litera-ture [39, 40]. While distal clavicle resection does offer theadvantage of potential avoidance of late osteoarthrosis, it

baFig. 15 Intraoperativephotographs from an ACseparation repair utilizing amodified Weaver–Dunntechnique. a The distal claviclehas been resected (asterisk). Inaddition, one end of anautologous graft has beenaffixed to the coracoid process.The other end (arrow) will beaffixed to the clavicle. b Theremaining end of the graft isaffixed to the clavicle,completing the reapproximationof the torn coracoclavicularligaments (photographs arecourtesy of the Department ofOrthopedic Surgery at theUniversity of SouthernCalifornia)

Fig. 16 Diagram of endobutton technique. An endobutton is insertedthrough surgically created tunnels in the clavicle and the coracoid(circle). This recreates the conoid portion of the CC ligament. A secondendobutton insertion may also be used to recreate the trapezoid portion.This procedure can also be performed in conjunction with a distalclavicular resection to prevent osteoarthrosis (arrow)

Fig. 17 Late osteoarthrosis. AP view of the right shoulder in a patientwith a chronic grade 3 AC separation. There is lucency and areas ofosteophytosis in the region of the distal clavicle. Numerous foci ofheterotopic ossification are also noted

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does increase the possibility of destabilization of the joint, apoint that should be kept in mind by the radiologist viewingthe postoperative imaging. Open or arthroscopic distal clav-icle resection may also be used in the rare instances of grade1 or 2 injury, which develop severe arthritic changes thatlimit the functionality of the joint [28]. At our institution, thepredominant method of choice for surgical reconstruction iscoracoclavicular fixation utilizing a double endobutton tech-nique (Fig. 16). Generally, this method of repair involvesplacement of a loop of synthetic material between the cor-acoid process and distal clavicle, allowing for joint strengthand stiffness equal to or greater than that of the nativeanatomy [41].

Imaging of potential postoperative complications

The imaging of the postsurgical AC joint will vary based onthe type of surgery that was performed, and knowledge ofthe surgical history is paramount to proper evaluation.

Expected postsurgical findings include near or completerestoration of the normal alignment of the AC joint with orwithout the presence of radiopaque hardware, partial resec-tion of the distal clavicle, and osseous tunneling related tograft placement. When present, the margin of the resecteddistal clavicle should be sharp and without evidence oflucency out of proportion to the patient’s overall bonemineralization. While there is variability in the amount ofclavicle resected, it has been shown that, in terms of pre-vention of complications, a resection margin of 0.8–1 cm isoptimal for prevention of postsurgical complications relatedto the resection. Resection margins above or below thisrange are more susceptible to complications related toover- or underresection, respectively [42]. A myriad ofpostoperative complications may occur, many of whichcan be readily diagnosed by the radiologist. The variousmethods of surgical reconstruction are geared toward pre-vention of these complications. The most common compli-cation is late osteoarthrosis. Findings on plain radiographysuggestive of the diagnosis include osteophyte formation

ba

Fig. 18 Osteolysis. a AP view of the left AC joint following endo-button repair of a grade 5 AC separation. Note the bone density of thedistal clavicle as well as the space between the distal clavicle and theacromion. b AP view of the left AC joint 5 months later. There is distalresorption of bone with widening of the AC interval, consistent with

osteolysis. Note the orientation of the more cranial endobutton haschanged. Though readily apparent in this patient, this case illustratesthe importance of utilizing baseline postoperative radiographs forcomparison when they are available

Fig. 19 Graft failure. a Baseline AP view of the left AC joint follow-ing endobutton fixation. b AP view of the left AC joint 7 months aftersurgery. Note the stretching of the graft as evidenced by increaseddistance between the radioopaque components of the endobutton graft.

Graft failure is a potential source of postsurgical instability of the ACjoint, as evidenced in this case by the increased craniocaudal intervalbetween the distal clavicle and the acromion

410 Emerg Radiol (2012) 19:399–413

and foci of heterotopic calcification (Fig. 17). Persistentinstability is another commonly encountered postsurgicalcomplication [41]. This instability may be related to a num-ber of different etiologies including postoperative osteolysisor graft insufficiency. When available, baseline radiographsfollowing surgery can be invaluable for proper evaluation ofpotential postsurgical pathology. These baseline studies canbe particularly useful when evaluating for osteolysis, as itcan be difficult to differentiate between the expected post-surgical AC interval and early osteolysis. However, overserial examinations, osteolysis will progress, while postop-erative changes should remain stable (Fig. 18). Furthermore,as subtle changes over time that may lead to instability willnot be readily appreciated on a single radiograph, a baselinecomparison can be extremely helpful in making this obser-vation on subsequent exams. When evaluating the postop-erative radiograph, the degree of widening of the joint spaceshould also be noted, as overzealous resection can contrib-ute to joint instability [40].

Graft insufficiency or rupture is another potential causeof post-surgical AC joint instability. Though the range ofincidence of graft failure varies by procedure and betweendifferent studies, overall graft failure leading to chronicsubluxation or disruption has been reported to be as high

as 30 % [43]. While some grafts have a radiopaquecomponent like an endobutton, other types of graftmaterial used for fixation may be radiolucent. It is thusimportant for the emergency radiologist to consider thispotential complication as a source of instability whenthere is abnormal alignment of the postoperative ACjoint, even in the absence of visible hardware or graftmaterial (Fig. 19).

Failure of the surgical hardware used for AC joint recon-struction can also be seen independent of or in conjunctionwith the aforementioned complications, emphasizing theimportance of prior imaging for comparison to insure theintegrity of the instrumentation. One such complicationincludes migration of the device used for or to support thefixation (Fig. 20). A more serious complication includes adelayed fracture at the surgical site, which can be seen oneither plain film or MDCT (Fig. 21). Postoperative infectionis a potential complication as well, and suspicion for thiscomplication may manifest itself on clinical exam. Althoughrare, damage to adjacent nerves, including the suprascapularnerve, or to blood vessels may occur during surgery. Injuriesto these structures are best evaluated with MRI and angio-graphic imaging, respectively. Recognition of these compli-cations is a crucial element of proper follow-up of the

Fig. 20 Hardware failure. a APview of the right AC jointfollowing endobuttonreconstruction of an ACseparation. Note the relationshipof the caudal endobutton to theinferior margin of the coracoids.b AP view of the right AC joint1 month later. The caudalendobutton has migratedsuperiorly, as evidenced by thenew position of the endobuttonrelative to the inferior marginof the coracoid

ba

Fig. 21 Fracture and tunnel widening. a AP view of the right AC jointfollowing endobutton reconstruction. Note the width of the tunnels aswell as the position of the endobuttons. b AP view of the right AC joint

1 year after surgery. There is tunnel widening (arrows), which mayhave precipitated endobutton migration (middle arrow). A fracture ofthe coracoid process is also present (circle)

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postsurgical shoulder, and it will often be the radiologistwho initially recognizes the complication.

Summary

Shoulder pain as a result of traumatic injury will continue toremain a common indication for presentation to the emer-gency room, and the role of the radiologist in the properdiagnosis of AC joint separations is essential. As the gradeof injury can profoundly impact the patient’s clinical man-agement, the radiologist must maintain familiarity with theclassification system for these injuries and with their appear-ances on various imaging modalities. Additionally, it is notuncommon for patients to present to the emergency roomcomplaining of new onset of pain or instability followingsurgical management. Thus, knowledge of the differentmethods of surgical correction, as well as their imagingappearances, is of utmost importance. Finally, as the sourceof the patient’s complaint may be the result of a postopera-tive complication, it is necessary to be able to distinguishthese entities from other potential causes of morbidity inorder to help direct appropriate patient care.

References

1. National Center for Health Statistics (2011) Health, United States,2010: with special feature on death and dying. National Center forHealth Statistics, Hyattsville

2. Bucholz RW, Heckman JD (2001) Rockwood and Green’sfractures in adults, Chapter 29: acromioclavicular joint inju-ries, 5th edn. Lippincott Williams & Wilkins, Philadelphia,PA, pp 1210–1244

3. Simovitch R, Sanders B, Ozbaydar M, Lavery K, Warner JJP(2009) Acromioclavicular joint injuries: diagnosis and manage-ment. J Am Acad Orthop Surg 17:207–219

4. Kaplan LD, Flanigan DC, Norwig J, Jost P, Bradley J (2005)Prevalence and variance of shoulder injuries in elite collegiatefootball players. Am J Sports Med 33:1142–1146

5. Alasaarela E, Tervonen O, Takalo R et al (1997) Ultrasoundevaluation of the acromioclavicular joint. J Rheumatol24:1959–1963

6. Iovane A, Midiri M, Galia M et al (2004) Acute traumatic acro-mioclavicular joint lesions: role of ultrasound versus conventionalradiography. Radiol Med 107:367–375

7. Williams PL, Bannister LH, Warwick R et al (1995) The anatom-ical basis of medicine and surgery. In: Gray H, Pick TP, Howden R(eds) Gray’s anatomy, 38th edn. Churchill Livingston, London, pp619–622

8. Lee KW, Debski RE, Chen CH et al (1997) Functional evaluationof the ligaments at the acromioclavicular joint during anteroposte-rior and superoinferior translation. Am J Sports Med 25:858–862

9. Antonio GE, Cho JH, Chung CB et al (2003) MR imaging appear-ance and classification of acromioclavicular joint injury. Am JRoentgen 180:1103–1110

10. Ernberg LA, Potter HG (2003) Radiographic evaluation of theacromioclavicular and sternoclavicular joints. Clin Sports Med22:255–275

11. Bossart PJ, Joyce SM, Manaster BJ et al (1988) Lack of efficacy of”weighted” radiographs in diagnosing acute acromioclavicularseparation. Ann Emerg Med 17:20–24

12. Vanarthos WJ, Ekman EF, Bohrer SP (1994) Radiographic diag-nosis of acromioclavicular joint separation without weight bearing:importance of internal rotation of the arm. Am J Roentgenol162:120–122

13. Beim GM (2000) Acromioclavicular joint injuries. J Athl Train35:261–267

14. Sluming VA (1995) A comparison of the methods of distraction forstress examination of the acromioclavicular joint. Br J Radiol68:1181–4

15. Vaatainen U, Pirinen A, Makela A (1991) Radiological evaluationof the acromioclavicular joint. Skeletal Radiol 20:115–116

16. Tossy JD, Mead MC, Sigmond HM (1963) AC separations: usefuland practical classification for treatment. Clin Orthop Relat Res28:111–119

17. Allman FL Jr (1967) Fractures and ligamentous injuries of theclavicle and its articulation. J Bone Joint Surg Am 49:774–784

18. Williams GR Jr, Nguyen VD, Rockwood CA Jr (1989) Classifica-tion and radiographic analysis of acromioclavicular dislocations.Appl Radiol 18:29–34

19. Lemos MJ (1998) The evaluation and treatment of the injuredacromioclavicular joint in athletes. Am J Sports Med 26:137–144

20. Alyas F, Curtis M, Speed C et al (2008) MR imaging appear-ances of the acromioclavicular joint dislocation. Radiographics28:463–479

21. Banerjee R, Waterman B, Padalecki J et al (2011) Manage-ment of distal clavicle fractures. J Am Acad Orthop Surg19:392–401

22. Fraser-Moodie JA, Shortt NL, Robinson CM (2008) Injuries to theacromioclavicular joint. J Bone Joint Surg Br 90-B:697–707

23. Scapinelli R (2004) Bipolar dislocation of the clavicle: 3D CTimaging and delayed surgical correction of a case. Arch OrthopTrauma Surg 124:421–424

24. Artingar E, Holzman M, Gunther S (2001) Bipolar claviculardislocation. Orthopedics 34:e316–319

25. Cote MP, Wojcik KE, Gomlinski G, Mazzocca AD (2010) Reha-bilitation of acromioclavicular separations: operative and nonop-erative considerations. Clin Sports Med 29:213–228

26. Gladstone J, Wilk K, Andrews J (1997) Nonoperative treatment ofacromioclavicular injuries. Oper Tech Sports Med 5:78–87

27. Bjerneld H, Hovelius L, Thorling J (1983) Acromio-clavicularseparations treated conservatively: a 5-year follow-up study. ActaOrthop Scand 54:743–745

28. Lervick GN (2005) Direct arthroscopic distal clavicle resection: atechnical review. Iowa Orthop J 25:149–156

29. Ponce BA, Millett PJ, Warner JJP (2004) Acromioclavicular jointinstability—reconstruction indications and techniques. OperativeTechniques in Sports Medicine 12:35–42

30. Spencer EE Jr (2007) Treatment of grade III acromioclavicularjoint injuries: a systematic review. Clin Orthop Relat Res455:38–44

31. Smith TO, Chester R, Pearse EO et al (2011) Operative versus non-operative management following Rockwood grade III acromiocla-vicular separation: a meta-analysis of the current evidence base. JOrthop Traumatol 12:19–27

32. Norrell H Jr, Llewellyn RC (1965) Migration of a threaded Stein-mann pin from an acromioclavicular joint into the spinal canal: acase report. J Bone Joint Surg Am 47:1024–1026

33. Sethi GK, Scott SM (1976) Subclavian artery laceration due tomigration of a Hagie pin. Surgery 80:644–646

34. Sim E, Schwarz N, Hocker K et al (1995) Repair of completeacromioclavicular separations using the acromioclavicular-hookplate. Clin Orthop Relat Res 314:134–142

412 Emerg Radiol (2012) 19:399–413

35. Liu HH, Chou YJ, Chen CH et al (2010) Surgical treatmentof acute acromioclavicular joint injuries using a modifiedWeaver–Dunn procedure and clavicular hook plate. Orthope-dics 33:552

36. Laprade RF, Wickum DJ, Griffith CJ, Ludewig PM (2008) Kine-matic evaluation of the modified Weaver–Dunn acromioclavicularjoint reconstruction. Am J Sports Med 36:2216–2221

37. Tauber M, Gordon K, Koller H, Fox M, Resch H (2009) Semite-ndinosus tendon graft versus a modified Weaver–Dunn procedurefor acromioclavicular joint reconstruction in chronic cases: a pro-spective comparative study. Am J Sports Med 37:181–190

38. Weaver JK, Dunn HK (1972) Treatment of acromioclavicularinjuries, especially complete acromioclavicular separation. J BoneJoint Surg Am 54:1187–1194

39. Snyder SJ, Banas MP, Karzel RP (1995) The arthroscopic Mum-ford procedure: an analysis of results. Arthroscopy 11:157–164

40. Stine IA, Vangsness CT Jr (2009) Analysis of the capsule andligament insertions about the acromioclavicular joint: a cadavericstudy. Arthroscopy 25:968–74

41. Struhl S (2007) Double endobutton technique for repair of com-plete acromioclavicular joint dislocations. Techniques in Shoulderand Elbow Surgery 4:175–179

42. Strauss EJ, Barker JU, McGill K et al (2010) The evaluation andmanagement of failed distal clavicle excision. Sports Med ArthroscRev 18:213–219

43. Thiel E, Mutnal A, Gilot G (2011) Surgical outcome followingarthroscopic fixation of acromioclavicular joint disruption with theTightRope device. Orthopedics 34:267

Emerg Radiol (2012) 19:399–413 413